The invention relates to an apparatus for facing an internal turning, comprising a housing rotating about an axis of rotation, at least one carriage displaceable in a guideway transversely to the axis of rotation and cutting tools arranged on the carriage.
Apparatuses of this type serve primarily for facing, i.e. for truing flat surfaces, and the internal turning, i.e. making bores having predetermined, in particular recessed cross-sectional contours, with two NC axes.
In know apparatuses of this type, the displacement of the carriages bearing the cutting tools, which determines the radius of operation of the cutting tool and, in particular, the diameter of the bore to be cut, is brought about by a drive derived from the rotation of spindle, in which the apparatus for facing and internal turning is itself secured. In addition, it is known to displace the carriage by means of an axially dispalceable pressure rod with the aid of helical gearing, the pressure rod hereby extending coaxially to the axis if rotation of the apparatus. It is also known to displace the carriage by means of a special electric motor which is arranged outside the rotating housing of the apparatus in a separate casing.
In order to adjust the carriages and the cutting tools borne thereby as accurately as possible it is necessary to measure exactly the distance each carriage is displaced. This distance is measured in all known apparatuses for facing and internal turning in an indirect manner. For example, the rotation, i.e. the angular distance, of a shaft which drives the carriages is measured and the distance travelled by the carriages deduced therefrom. Inaccuracies may, however, occur during distance measurement, for example due to unavoidable tolerances, and these inaccuracies have a negative influence on the exact positioning of the cutting tools and on the repeatability of a setting. A further disadvantage of the known apparatus for facing and internal turning is to be seen in the fact that the drive means which are arranged outside the rotating housing of the apparatus and provided for displacement of the carriages are complicated and bulky which has an unfavourable effect on the machining performance to be attained with this apparatus.